Solar cell and photovoltaic module

ABSTRACT

A solar cell and a photovoltaic module including the same are provided. The solar cell includes a substrate having a first surface and a second surface opposite to each other; a first passivation stack disposed on the first surface and including a first oxygen-rich dielectric layer, a first silicon-rich dielectric layer, a second oxygen-rich dielectric layer, and a second silicon-rich dielectric layer that are sequentially disposed in a direction away from the first surface, wherein an atomic fraction of oxygen in the first oxygen-rich dielectric layer is less than an atomic fraction of oxygen in the second oxygen-rich dielectric layer; a tunneling oxide layer disposed on the second surface; a doped conductive layer disposed on a surface of the tunneling oxide layer; and a second passivation layer disposed on a surface of the doped conductive layer.

CROSS-REFERENCE TO RELATED APPLICATION

The application claims priority to Chinese Patent Application No.202110963291.4, filed on Aug. 20, 2021, the content of which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments of the present disclosure relate to the photovoltaic field,in particular to a solar cell and a photovoltaic module.

BACKGROUND

Potential induced degradation (PID) refers to a phenomenon of powerdegradation of photovoltaic module under a long-term action of externalvoltage. At present, PID-s and PID-p theory are generally employed forthe failure mechanism of PID. According to the PID-s theory,ethylene-vinyl acetate (EVA) in package material is hydrolyzed byreacting with water vapor to produce acetic acid which then reacts witha glass surface to produce free sodium ions Na+, and under action ofelectric field, the sodium ions Na+ penetrate through a passivationlayer and enter a PN junction, so that a leakage path is formed.According to the PID-p theory, carrier recombination is caused by thesodium ions Na+ attracting minority carriers on the back.

SUMMARY

In one aspect, embodiments of the present disclosure provide a solarcell including a substrate, a first passivation stack, a tunneling oxidelayer, a doped conductive layer and a second passivation layer. Thesubstrate has a first surface and a second surface opposite to eachother. The first passivation stack is disposed on the first surface andincludes a first oxygen-rich dielectric layer, a first silicon-richdielectric layer, a second oxygen-rich dielectric layer, and a secondsilicon-rich dielectric layer that are sequentially disposed in adirection away from the first surface. An atomic fraction of oxygen inthe first oxygen-rich dielectric layer is less than an atomic fractionof oxygen in the second oxygen-rich dielectric layer. The tunnelingoxide layer is disposed on the second surface. The doped conductivelayer is disposed on a surface of the tunneling oxide layer. The secondpassivation layer is disposed on a surface of the doped conductivelayer.

In an embodiment, both the first silicon-rich dielectric layer and thesecond silicon-rich dielectric layer includes oxygen atoms, the atomicfraction of oxygen in the first oxygen-rich dielectric layer is in arange of 40% to 70%, the first silicon-rich dielectric layer includesoxygen atoms and an atomic fraction of oxygen in the first silicon-richdielectric layer is greater than 0% and less than or equal to 10%, theatomic fraction of oxygen in the second oxygen-rich dielectric layer isin a range of 30% to 80%, and the second silicon-rich dielectric layerincludes oxygen atoms and an atomic fraction of oxygen in the secondsilicon-rich dielectric layer is greater than 0% and less than or equalto 10%.

In an embodiment, the atomic fraction of oxygen in the first oxygen-richdielectric layer is in a range of 40% to 60%, the atomic fraction ofoxygen in the first silicon-rich dielectric layer is greater than 0% andless than or equal to 7%, the atomic fraction of oxygen in the secondoxygen-rich dielectric layer is in a range of 50% to 80%, and the atomicfraction of oxygen in the second silicon-rich dielectric layer isgreater than 0% and less than or equal to 7%.

In an embodiment, a material of the first oxygen-rich dielectric layerincludes at least one and aluminum oxide, silicon oxide, siliconoxynitride, gallium oxide, titanium oxide, or hafnium oxide.

In an embodiment, the first oxygen-rich dielectric layer includes analuminum oxide layer and a silicon oxynitride layer, and the aluminumoxide layer is positioned between the silicon oxynitride layer and thesubstrate.

In an embodiment, a ratio of the number of oxygen atoms to the number ofaluminum atoms in the aluminum oxide is in a range of 0.6 to 2.4.

In an embodiment, a refractive index of the first oxygen-rich dielectriclayer is higher than a refractive index of the second oxygen-richdielectric layer.

In an embodiment, the first oxygen-rich dielectric layer includes asilicon oxide material, a refractive index of the first oxygen-richdielectric layer is in a range of 1.58 to 1.61, and a thickness of thefirst oxygen-rich dielectric layer in a direction perpendicular to thefirst surface is in a range of 2 nm to 15 nm.

In an embodiment, the first oxygen-rich dielectric layer includes asilicon oxynitride material, a refractive index of the first oxygen-richdielectric layer is in a range of 1.61 to 1.71, and a thickness of thefirst oxygen-rich dielectric layer in a direction perpendicular to thefirst surface is in a range of 8 nm to 20 nm.

In an embodiment, the first oxygen-rich dielectric layer includes analuminum oxide material, a refractive index of the first oxygen-richdielectric layer is in a range of 1.71 to 1.81, and a thickness of thefirst oxygen-rich dielectric layer in a direction perpendicular to thefirst surface is in a range of 1 nm to 20 nm.

In an embodiment, the second oxygen-rich dielectric layer includes asilicon oxynitride material, a refractive index of the secondoxygen-rich dielectric layer is in a range of 1.56 to 1.62, and athickness of the second oxygen-rich dielectric layer in a directionperpendicular to the first surface is in a range of 5 nm to 20 nm.

In an embodiment, a refractive index of the first silicon-richdielectric layer is higher than a refractive index of the secondsilicon-rich dielectric layer.

In an embodiment, the refractive index of the first silicon-richdielectric layer is in a range of 2.02 to 2.2, and the refractive indexof the second silicon-rich dielectric layer is in a range of 1.98 to2.06.

In an embodiment, a material of the first silicon-rich dielectric layerincludes a first silicon nitride material, and a ratio of the number ofsilicon atoms to the number of nitrogen atoms in the first siliconnitride material is in a range of 0.66 to 2.3.

In an embodiment, a refractive index of the first silicon-richdielectric layer is in a range of 2.02 to 2.2, and a thickness of thefirst silicon-rich dielectric layer in a direction perpendicular to thefirst surface is in a range of 20 nm to 50 nm.

In an embodiment, a material of the second silicon-rich dielectric layerincludes a second silicon nitride material, and a ratio of the number ofsilicon atoms to the number of nitrogen atoms in the second siliconnitride material is in a range of 0.46 to 1.87.

In an embodiment, a refractive index of the second silicon-richdielectric layer is in a range of 1.98 to 2.06, and a thickness of thesecond silicon-rich dielectric layer in a direction perpendicular to thefirst surface is in a range of 20 nm to 50 nm.

In an embodiment, a refractive index of the second passivation layer isin a range of 2.04 to 2.2, and a thickness of the second passivationlayer in a direction perpendicular to the second surface is in a rangeof 60 nm to 100 nm.

In another aspect, embodiments of the present disclosure provide aphotovoltaic module including a cell string, a package adhesive film anda cover plate. The cell string includes a plurality of solar cellsconnected with each other. The package adhesive film is configured tocover a surface of the cell string. The cover plate is configured tocover a surface of the package adhesive film facing away from the cellstring. Each of the plurality of solar cells includes a substrate, afirst passivation stack, a tunneling oxide layer, a doped conductivelayer and a second passivation layer. The substrate has a first surfaceand a second surface opposite to each other. The first passivation stackis disposed on the first surface and includes a first oxygen-richdielectric layer, a first silicon-rich dielectric layer, a secondoxygen-rich dielectric layer, and a second silicon-rich dielectric layerthat are sequentially disposed in a direction away from the firstsurface. An atomic fraction of oxygen in the first oxygen-richdielectric layer is less than an atomic fraction of oxygen in the secondoxygen-rich dielectric layer. The tunneling oxide layer is disposed onthe second surface. The doped conductive layer is disposed on a surfaceof the tunneling oxide layer. The second passivation layer is disposedon a surface of the doped conductive layer.

In an embodiment, the photovoltaic module further includes an edgesealing member fixedly packaging at least the sides of the photovoltaicmodule.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments are described as examples with reference to thecorresponding figures in the accompanying drawings, and the examples donot constitute a limitation to the embodiments. Elements with the samereference numerals in the accompanying drawings represent similarelements. The figures in the accompanying drawings do not constitute aproportion limitation unless otherwise stated.

FIG. 1 is a schematic cross-sectional view of a solar cell according toan embodiment of the present disclosure.

FIG. 2 is a partial sectional view of a solar cell according to anembodiment of the present disclosure.

FIG. 3 is a schematic diagram showing atomic fraction of various atomsin different positions of a solar cell according to an embodiment of thepresent disclosure.

FIGS. 4 and 5 are schematic structural diagrams of a photovoltaic moduleaccording to an embodiment of the present disclosure.

FIGS. 6 to 10 are schematic structural diagrams corresponding to varioussteps of a method for manufacturing a solar cell according to theembodiment of the present disclosure.

DETAILED DESCRIPTION

The embodiments of the present disclosure will be described in detailbelow with reference to the accompanying drawings in order to make theobjectives, technical solutions and advantages of the present disclosureclearer. However, those skilled in the art may appreciate that, in thevarious embodiments of the present disclosure, numerous technicaldetails are set forth in order to provide the reader with a betterunderstanding of the present disclosure. However, the technicalsolutions claimed in the present disclosure may be implemented withoutthese technical details and various changes and modifications based onthe following embodiments.

The embodiments of the present disclosure provide a solar cell and aphotovoltaic module. The solar cell provided in the embodiments of thepresent disclosure will be described in detail below with reference tothe accompanying drawings. FIG. 1 is a schematic cross-sectional view ofa solar cell according to an embodiment of the present disclosure. FIG.2 is a partial sectional view of a solar cell according to an embodimentof the present disclosure. FIG. 3 is a schematic diagram showingfraction of various atoms in different positions of a solar cellaccording to an embodiment of the present disclosure.

Referring to FIG. 1 , the solar cell includes a substrate 10, a firstpassivation stack, a tunneling oxide layer 121, a doped conductive layer122 and a second passivation layer 123. The substrate 10 has twoopposite surfaces, i.e., a first surface 10 a and a second surface 10 b.The first passivation stack is disposed on the first surface 10 a. Thefirst passivation stack includes a first oxygen-rich dielectric layer111, a first silicon-rich dielectric layer 112, a second oxygen-richdielectric layer 113, and a second silicon-rich dielectric layer 114that are sequentially disposed in a direction away from the firstsurface 10 a. An atomic fraction of oxygen in the first oxygen-richdielectric layer 111 is less than that in the second oxygen-richdielectric layer 113. The tunneling oxide layer 121 is disposed on thesecond surface 10 b. The doped conductive layer 122 disposed on asurface of the tunneling oxide layer 121. The second passivation layer123 is disposed on a surface of the doped conductive layer 122.

It should be noted that the oxygen-rich dielectric layer is a relativeconcept to which an oxygen-deficient dielectric layer is opposite, andthe silicon-rich dielectric layer is a relative concept to which asilicon-deficient dielectric layer is opposite. In a local environment,a dielectric layer of a relatively large atomic fraction of oxygen maybe referred to as the oxygen-rich dielectric layer, a dielectric layerof a relatively small atomic fraction of oxygen or an oxygen-freedielectric layer may be referred to as the oxygen-deficient dielectriclayer. Similarly, a dielectric layer of a relatively large atomicfraction of silicon may be referred to as the silicon-rich dielectriclayer, a dielectric layer of a relatively small atomic fraction ofsilicon or a silicon-free dielectric layer may be referred to as thesilicon-deficient dielectric layer. A numerical value of the atomicfraction of oxygen in the oxygen-rich dielectric layer and a numericalvalue of the atomic fraction of silicon in the silicon-rich dielectriclayer are not limited herein.

Compared with the silicon-rich dielectric layer, the oxygen-richdielectric layer may be of higher density, weaker positive electricityand lower hardness, which contribute to preventing external ions fromdiffusing into the substrate and to reducing stress damage on thesubstrate, or may be of stronger negative electricity, which contributesto forming field passivation on the substrate and realizing selectivetransmission of carriers. At least two oxygen-rich dielectric layers areprovided, which may strengthen any one of the aforementioned effects ormake the solar cell have both effects. In addition, compared with theoxygen-rich dielectric layer, the silicon-rich dielectric layergenerally has a higher refractive index. The two silicon-rich dielectriclayers are spaced from each other, which is advantageous for causing twogradients of refractive index, that is, a first gradient of refractiveindex caused by the second silicon-rich dielectric layer and an externalfilm layer (for example, a package film layer and a cover plate), and asecond gradient of refractive index caused by the first silicon-richdielectric layer and the second oxygen-rich dielectric layer, so thatlight of different wavelengths can effectively enter into the substrate,which is advantageous for improving the absorption efficiency of thesolar cell.

Further, the atomic fraction of oxygen in the first oxygen-richdielectric layer 111 is less than that in the second oxygen-richdielectric layer 113. Since the larger the atomic fraction of oxygen,the stronger the compactness of the corresponding layer, and the betterthe barrier performance to the external ions or other impurities, thesecond oxygen-rich dielectric layer 113 of larger atomic fraction ofoxygen contributes to blocking the external ions or other impurities inthe outer layer, avoiding influence on antireflection performance of thefirst silicon-rich dielectric layer 112, and ensuring a higherefficiency for light absorption of the solar cell.

The solar cell shown in FIG. 1 will be described in more detail belowwith reference to the accompanying drawings.

In some embodiments, the substrate 10 is made from silicon-basedmaterial, such as one or more of monocrystalline silicon, polysilicon,amorphous silicon, or microcrystalline silicon. In other embodiments,the substrate may be made from material, such as carbon in simplesubstance, organic material, or multinary-compound, and themultinary-compound may include, but are not limited to, perovskite,gallium arsenide, cadmium telluride, copper indium selenium, and thelike.

In some embodiments, the first surface 10 a is a light receivingsurface, the second surface 10 b is a rear surface opposite to the lightreceiving surface. The first surface 10 a may be a pyramid-texturedsurface to reduce light reflection on the first surface 10 a, increaselight absorption and utilization, and improve conversion efficiency ofthe solar cell. In some embodiments, the second surface 10 b may alsofunction as a light receiving surface when the solar cell is adouble-sided cell.

The substrate 10 includes a base region 101 and an emitter 102. In someembodiments, the solar cell is an N-type cell, such as a TOPCon (TunnelOxide Passivated Contact) cell, in which the base region 101 includes anN-type doped element (e.g., phosphorus, arsenic, antimony, etc.), theemitter 102 includes a P-type doped element, the emitter 102 and thebase region 101 form a PN junction, and the first oxygen-rich dielectriclayer 111 covers the first surface 10 a. In other embodiments, the solarcell is a P-type cell, such as a PERC (Passivated Emitter and RearCell), in which the base region includes a P-type doped element (e.g.,boron, indium, etc.), the emitter includes an N-type doped element, theemitter and the base region form a PN junction, and the firstoxygen-rich dielectric layer covers the second surface. The solar cellis described in detail below by taking the TOPCon cell as an example.

In some embodiments, the material of the first oxygen-rich dielectriclayer 111 includes at least one of aluminum oxide, silicon oxide,silicon oxynitride, gallium oxide, titanium oxide, and hafnium oxide.Since the first oxygen-rich dielectric layer 111 may include materialsof different electrical properties with different functions, thefunctions of the first oxygen-rich dielectric layer 111 may be discussedbased on different material compositions, as follows:

In some embodiments, the first oxygen-rich dielectric layer 111 is ofnegative electricity, and the first oxygen-rich dielectric layer 111includes at least one of aluminum oxide, gallium oxide, titanium oxide,and hafnium oxide, so as to form field passivation on the substrate 10,facilitate selective transmission of carriers, reduce carrierrecombination, and improve photoelectric conversion efficiency. On thisbasis, the atomic fraction of oxygen in the first oxygen-rich dielectriclayer 111 may be in a range of 40% to 70%, for example, 45%, 50%, 55%,60%, or 65%. When the atomic fraction of oxygen is too low, the firstoxygen-rich dielectric layer 111 is of weaker negative electricity andhigher hardness. The weaker negative electricity is disadvantageous fordangling bonds at the saturation interface and to suppression of carrierrecombination, and the higher hardness is disadvantageous for reductionof the stress damage between the substrate 10 and the first oxygen-richdielectric layer 111. When the atomic fraction of oxygen is too high,the first oxygen-rich dielectric layer 111 is of stronger negativeelectricity, which prevents migration and permeation of externalpositive ions into the substrate. As an example, the atomic fraction ofoxygen in the first oxygen-rich dielectric layer 111 may be in a rangeof 40% to 60%.

When the edge of the photovoltaic module gets damp, the EVA material inthe package material is hydrolyzed by reacting with water vapor toproduce acetic acid, and the acetic acid reacts with the cover glass toproduce free sodium ions Na+. Under action of electric field, the sodiumions Na+ pass through the passivation layer and destroys the PN junctionto form a leakage path. When being made from a material of negativeelectricity, such as aluminum oxide, the first oxygen-rich dielectriclayer 111 carries charges whose polarity is opposite to that of thesodium ions Na+, so that it is impossible to prevent permeation andmigration of the sodium ions Na+ by polarity repulsion, and the sodiumions Na+ may even be attracted to move toward the substrate, which aredisadvantageous for protecting the PN junction. By controlling thenegative electricity of the first oxygen-rich dielectric layer 111within a certain range with reasonable composition of the firstoxygen-rich dielectric layer 111, it is advantageous for suppression ofan attractive force applied by the first oxygen-rich dielectric layer111 to the sodium ions Na+, so as to improve the electrical property ofthe PN junction.

In some embodiments, the material of the first oxygen-rich dielectriclayer 111 includes at least one of silicon oxide and silicon oxynitride.If the base region 101 includes mainly a semiconductor element, such asa silicon element, the first oxygen-rich dielectric layer 111 includeselements having properties similar to that of the substrate 10, and thematerial property of the first oxygen-rich dielectric layer 111 aresimilar to the material property of the substrate 10. As a result,stress damage and interface defects caused by difference in materialproperty between the first oxygen-rich dielectric layer 111 and thesubstrate 10 are reduced, and the transmission efficiency ofphotogenerated carriers is improved.

In addition, the first oxygen-rich dielectric layer 111 is of positiveelectricity and high density when being mainly made from at least one ofsilicon oxide and silicon oxynitride, both of which are generally ofpositive electricity and high density, thereby preventing penetration ofthe sodium ions Na+. On this basis, the atomic fraction of oxygen in thefirst oxygen-rich dielectric layer 111 may be in a range of 40% to 70%,for example, 45%, 50%, 55%, 60%, or 65%. When the atomic fraction ofoxygen is too low, the first oxygen-rich dielectric layer 111 is ofstronger positive electricity, and majority carriers may fill holes inthe first oxygen-rich dielectric layer 111 or react with doped hydrogenions, which is disadvantageous for suppression of carrier recombination.When atomic fraction of oxygen is too high, the first oxygen-richdielectric layer 111 is of low refractive index, which may enhancereflection and emission of the incident light and thus isdisadvantageous for improving the light absorption efficiency.

In some embodiments, the first oxygen-rich dielectric layer 111 includesboth a material of positive electricity (e.g., silicon oxide) and amaterial of negative electricity (e.g., aluminum oxide), and the atomicfraction of oxygen in the first oxygen-rich dielectric layer 111 is in arange of 40% to 70%, for example, 45%, 50%, 55%, 60%, or 65%, such thatthe first oxygen-rich dielectric layer 111 has both advantages of thetwo materials, that is, the first oxygen-rich dielectric layer 111 is ofnegative electricity, can form field passivation on the substrate 111and achieve selective transmission of carriers; and meanwhile, the firstoxygen-rich dielectric layer 111 is of high density, which isadvantageous for preventing penetration of sodium ions; in addition, thematerial property of the first oxygen-rich dielectric layer 111 aresimilar to the material property of the substrate 111, such that thestress damage caused by the first oxygen-rich dielectric layer 111 tothe substrate 111 is reduced; moreover, the rich oxygen atoms can bindto the unsaturated silicon atoms on the first surface 10 a, such thatthe density of the hanging bonds is reduced, the carrier recombinationis suppressed, and the photoelectric conversion efficiency is improved.

In some embodiments, the material of positive electricity and thematerial of negative electricity in the first oxygen-rich dielectriclayer 111 are mixed with each other without a clear boundary. In otherembodiments, the first oxygen-rich dielectric layer 111 has amulti-layer structure, as shown in FIG. 2 , the first oxygen-richdielectric layer 111 includes an aluminum oxide layer and a siliconoxynitride layer, and the aluminum oxide layer is disposed between thesilicon oxynitride layer and the substrate.

FIG. 3 is an example of elemental analysis for the first passivationstack of the solar cell according to an embodiment. Referring to FIG. 3, a position section of 0-37.5 nm, in which the silicon element is themajority, refers to the substrate 10; a position section of 37.5-50 nm,in which the oxygen element and the aluminum element are the majority,refers to the aluminum oxide layer in the first oxygen-rich dielectriclayer 111; a position section of 50-53 nm, in which the atomic fractionof oxygen and the atomic fraction of aluminum decrease gradually and theatomic fraction of silicon and the atomic fraction of nitrogen increasegradually, means that the silicon nitride layer is to be formed on thealuminum oxide layer, but it is noteworthy that the atomic fraction ofnitrogen decreases suddenly near a position of 52 nm, which may becaused by sputtering of the oxygen element in the aluminum oxide layerand then mixing of the oxygen element with the nitrogen ions and thesilicon ions due to the bombardment of the nitrogen ion source and thesilicon ion source having specific contents, and finally forming a thinsilicon oxynitride layer; a position section of 53-85 nm and a positionsection of 90-125 nm, in which the nitrogen element and the siliconelement are the majority, respectively refer to the first silicon-richdielectric layer 112 including a first silicon nitride material and thesecond silicon-rich dielectric layer 114 including a second siliconnitride material; a position section of 85-90 nm, in which the oxygenelement and the silicon element are the majority and the proportion ofthe atomic fraction of silicon decreases by a certain extent withrespect to both sides, refers to the second oxygen-rich dielectric layer113, and the atomic fraction of oxygen in the second oxygen-richdielectric layer 113 is greater than the atomic fraction of silicon inthe first silicon-rich dielectric layer 112 and the second silicon-richdielectric layer 114. In addition, both the first oxygen-rich dielectriclayer 111 and the second oxygen-rich dielectric layer 113 have a peak inthe atomic fraction of oxygen, which indicates that the oxygen elementmigrates and permeates into adjacent layer(s). Similarly, the atomicfraction of nitrogen in the first silicon-rich dielectric layer 112 andthe second silicon-rich dielectric layer 114 gradually increases andthen gradually decreases, which indicates that the nitrogen elementmigrates and permeates into adjacent layer(s). The silicon oxynitridelayer can reduce stress damage and interface defects between aluminumoxide layer and silicon nitride layer, suppress carrier recombinationand improve photoelectric conversion efficiency of the solar cell.

It should be noted that, whether the first oxygen-rich dielectric layer111 is of single-layer structure or multi-layer structure, when thefirst oxygen-rich dielectric layer 111 includes mainly aluminum oxidematerial, based on consideration of both the negative electricity andthe hardness, it is necessary to limit the composition proportion of thealuminum oxide material covering the first surface 10 a, for example, bysetting a ratio of the number of oxygen atoms to the number of aluminumatoms to be in a range of 0.6 to 2.4, for example, 1, 1.5, or 2, so thatthe negative electricity of the first oxygen-rich dielectric layer 111is controlled within a reasonable range, thereby balancing the fieldpassivation effect of the aluminum oxide material on the substrate 111and the attractive force applied by the aluminum oxide to the sodiumions Na+, and ensuring that the first oxygen-rich dielectric layer 111has a higher density and a lower hardness, so that the first oxygen-richdielectric layer 111 has a better blocking effect to the sodium ions Na+and that the first oxygen-rich dielectric layer 111 applies a lowerstress to the substrate 111.

For example, a refractive index of the first oxygen-rich dielectriclayer 111 may be in a range of 1.71 to 1.81, for example, 1.173, 1.76,and 1.79, and a thickness of the first oxygen-rich dielectric layer 111in a direction perpendicular to the first surface 10 a may be in a rangeof 1 nm to 20 nm, particularly, 5 nm to 10 nm, for example, 6 nm, 7 nm,8 nm, or 9 nm.

Further, when the first oxygen-rich dielectric layer 111 includes atleast one of silicon oxide and silicon oxynitride, based onconsideration of both the positive electricity and the density, thecontent of different elements in the first oxygen-rich dielectric layer111 needs to be limited, specifically, the refractive index of the firstoxygen-rich dielectric layer 111 needs to be limited. Meanwhile, sincesilicon oxide is of higher compactness and thus better barrier propertycompared with silicon oxynitride, in order to make the first oxygen-richdielectric layer 111 including silicon oxynitride meet a presetrequirement for barrier property, the first oxygen-rich dielectric layer111 including silicon oxynitride needs to have a relatively thickthickness.

For example, the first oxygen-rich dielectric layer 111 includes asilicon oxide material, the refractive index of the first oxygen-richdielectric layer 111 is in a range of 1.58 to 1.61, for example, 1.59,or 1.60, and the thickness of the first oxygen-rich dielectric layer 111in the direction perpendicular to the first surface 10 a is in a rangeof 2 nm to 15 nm, for example, 5 nm, 8 nm, 10 nm, or 13 nm.Alternatively, the first oxygen-rich dielectric layer 111 includes asilicon oxynitride material, the refractive index of the firstoxygen-rich dielectric layer 111 is in a range of 1.61 to 1.71, forexample, 1.62, 1.65, or 1.68, and the thickness of the first oxygen-richdielectric layer 111 in the direction perpendicular to the first surface10 a is in a range 8 nm to 15 nm, for example, 10 nm, 12 nm, or 14 nm.

In some embodiments, the first oxygen-rich dielectric layer 111including a silicon oxide material may be formed by oxidizing thesubstrate 10 in an oxygen-rich atmosphere, a process temperaturetherefor may be in a range of 450° C. to 500° C., for example, 460° C.,470° C., 480° C., or 490° C., a process time therefor may be in a rangeof 15 min to 30 min, for example, 18 min, 23 min, or 28 min, and avolume ratio of oxygen in the oxygen-rich atmosphere may be greater than21% to ensure a higher density of the silicon oxide material. Meanwhile,the silicon oxide material may be formed on the surface of the substrate10 by ozone oxidation, nitrous oxide oxidation, or nitric acidpassivation. A layer of negative electricity including at least some ofaluminum oxide, gallium oxide, titanium oxide, or hafnium oxide or thefirst oxygen-rich dielectric layer 111 may be formed by atomic layerdeposition and plasma-enhanced deposition, so that the layer of negativeelectricity has a higher density.

In some embodiments, the material of the second oxygen-rich dielectriclayer 113 includes at least one of silicon oxide and silicon oxynitride.The atomic fraction of oxygen in the second oxygen-rich dielectric layer113 is controlled to be in a range of 30% to 80%, for example, 40%, 50%,60%, or 70%, which renders an appropriate range of refractive index forthe second oxygen-rich dielectric layer 113, as a low refractive indexmay cause internal reflection and emission of the incident light throughthe second silicon-rich dielectric layer 114. It can be understood that,when the absorption rate of the short wave is low, the photovoltaicmodule presents blue or dark blue, which is disadvantageous forpreparing the photovoltaic module having a black appearance. As anexample, the atomic fraction of oxygen in the second oxygen-richdielectric layer 113 is in a range of 50% to 80%.

In some embodiments, the refractive index of the second oxygen-richdielectric layer 113 is lower so as to make the incident light fallingon the substrate 10 as vertically as possible. That is, the refractiveindex of the first oxygen-rich dielectric layer 111 is larger than therefractive index of the second oxygen-rich dielectric layer 113, and therefractive index of the first silicon-rich dielectric layer 112 islarger than the refractive index of the second oxygen-rich dielectriclayer 113, so that the incident light enters the substrate 10 asvertically as possible after passing through the second oxygen-richdielectric layer 113, the first silicon-rich dielectric layer 112 andthe first oxygen-rich dielectric layer 111, which reduces internalreflection and emission of the light, and improves the light absorptionefficiency of the solar cell. As an example, the refractive index rangeof the first oxygen-rich dielectric layer 111 may be in a range of 1.58to 1.78, for example, 1.63, 1.68, or 1.73, and the refractive index ofthe second oxygen-rich dielectric layer 113 may be in a range of 1.56 to1.62, for example, 1.57, or 1.59.

In the direction perpendicular to the first surface 10 a, the thicknessof the first oxygen-rich dielectric layer 111 may be greater than thethickness of the second oxygen-rich dielectric layer 113, and thethickness of the first silicon-rich dielectric layer 112 may be greaterthan the thickness of the second oxygen-rich dielectric layer 113, so asto satisfy the aforementioned relationship between the refractiveindexes. In this way, it is advantageous for the first silicon-richdielectric layer 112 to mainly absorb long-wave light, and for the firstoxygen-rich dielectric layer 111 and the second oxygen-rich dielectriclayer 113 to mainly absorb short-wave light of various wavelengths, soas to ensure a higher light absorption efficiency of the solar cell fordifferent wavelength bands, and make the photovoltaic module to have ablack appearance.

In some embodiments, the second oxygen-rich dielectric layer 113includes a silicon oxynitride material. The refractive index of thesecond oxygen-rich dielectric layer 113 is in a range of 1.56 to 1.62,for example, 1.57, or 1.59. In the direction perpendicular to the firstsurface 10 a, the thickness of the second oxygen-rich dielectric layer113 is in a range of 5 nm to 20 nm, particularly, 5 nm to 18 nm, forexample, 7 nm, 10 nm, 13 nm, or 16 nm. Based on the requirements of therefractive index of the second oxygen-rich dielectric layer 113, theratio of the number of oxygen atoms to the number of nitrogen atoms inthe silicon oxynitride material may be in a range of 2.58 to 7.58, forexample, 3.5, 4.5, 5.5, or 6.5. The nitrogen element in the siliconoxynitride material may be derived from preparation process or may bederived from element diffusion of adjacent layer(s). The presence of thenitrogen element contributes to improve the refractive index of thesecond oxygen-rich dielectric layer 113, suppress the internalreflection due to low refractive index, improve matching of the secondnitrogen-rich dielectric layer 113 with the adjacent layer(s) includinga silicon nitride material, and reduce a contact stress between thesecond nitrogen-rich dielectric layer 113 and the adjacent layer(s).

In some embodiments, the refractive index of the first silicon-richdielectric layer 112 is greater than the refractive index of the secondsilicon-rich dielectric layer 114, which reduces difference between therefractive indexes of the second silicon-rich dielectric layer 114 andthe second oxygen-rich dielectric layer 113, thus reduce internalreflection and emission of the light due to the difference between therefractive indexes. Further, it is advantageous to make the refractiveindex of the first silicon-rich dielectric layer 112 larger than therefractive index of the second oxygen-rich dielectric layer 113, whichincreases a gradient of refractive index, thereby ensuring effectivelyincident light on the substrate, and improving the light absorptionefficiency of the solar cell. As an example, the refractive index of thefirst silicon-rich dielectric layer 112 may be in a range of 2.02 to2.2, for example, 2.04, 2.06, 2.10, 2.14, or 2.18, and the refractiveindex of the second silicon-rich dielectric layer 114 may be in a rangeof 1.98 to 2.06, for example, 2.00, 2.02, or 2.04.

Accordingly, the thickness of the first silicon-rich dielectric layer112 may be greater than the thickness of the second silicon-richdielectric layer 114 in a direction perpendicular to the surface of thesubstrate 10 to satisfy the aforementioned relationship of therefractive indexes. In this way, it is advantageous for the firstsilicon-rich dielectric layer 112 and the second silicon-rich dielectriclayer 114 to mainly absorb the long-wave light of different wavelengths,thereby improving the light absorption efficiency of the solar cell fordifferent wavelength bands.

In some embodiments, the material of the first silicon-rich dielectriclayer 112 includes nitrogen silicide. During determination on atomicfraction of element in the first silicon-rich dielectric layer 112, itis necessary to prevent the first silicon-rich dielectric layer 112 frombeing of excessively strong positive electricity (which diminishes thefield passivation effect of the first oxygen-rich dielectric layer 111and/or the electrical property of the emitter 102), and meanwhile it isnecessary to prevent the first silicon-rich dielectric layer 112 frombeing of excessively weak positive electricity (which is disadvantageousfor blocking of the sodium ions Na+ by electricity repulsion), ofexcessively low refractive index (which is likely to cause internalreflection and emission of the light), or of excessively low compactness(which is also disadvantageous for blocking of the sodium ions Na+ byelectricity repulsion). Based on the above considerations, the firstsilicon-rich dielectric layer 112 includes a first silicon nitridematerial in which a ratio of the number of silicon atoms to the numberof nitrogen atoms is in a range of 0.66 to 2.3, example, 1.1, 1.6, or2.1.

To enable the different layers to mainly absorb light of differentwavelengths and to enable the light incident through the secondoxygen-rich dielectric layer 113 to better enter the substrate 10, underthe condition of the aforementioned ratio of atoms, the refractive indexof the first silicon-rich dielectric layer 112 may be in a range of 2.02to 2.2, for example, 2.04, 2.06, 2.10, 2.14, or 2.18, a thickness of thefirst silicon-rich dielectric layer 112 in the direction perpendicularto the first surface 10 a is in a range of 20 nm to 50 nm, particularly,20 nm to 40 nm, for example, 25 nm, 30 nm, or 35 nm. The firstsilicon-rich dielectric layer 112 should be thick enough to refract thelight into the substrate 10, and should be thin enough to preventapplying an excessive stress to the first oxygen-rich dielectric layer111, to avoid interface defects, and to reduce an overall size of thesolar cell.

The first silicon-rich dielectric layer 112 may be an oxygen-dopedsilicon nitride layer in which the atomic fraction of oxygen isrelatively small, that is, the first silicon-rich dielectric layer 112is a silicon-rich oxygen-deficient dielectric layer (which may also bereferred to as a first silicon-rich oxygen-deficient dielectric layer).In some embodiments, the oxygen atoms are derived from an adjacentoxygen-rich dielectric layer, and the oxygen atoms in the adjacentoxygen-rich dielectric layer diffuse into the first silicon-richdielectric layer 112 based on a set process, for example, byconcentration difference or thermal energy imparted based on a heattreatment process. In other embodiments, the oxygen atoms are derivedfrom residual oxygen source gas in the reaction chamber or designedlyreserved oxygen source gas.

The first oxygen-rich dielectric layer 111 and the first silicon-richdielectric layer 112 may be successively formed in the same reactionchamber. Before the first silicon-rich dielectric layer 112 is formed,if a duration for purging process is not long enough or a part of areactant is attached to a side wall of the reaction chamber, oxygenatoms may remain in the reaction chamber. During the formation of thefirst silicon-rich dielectric layer 112, the oxygen atoms may be dopedinto the silicon nitride material, thereby forming oxygen-doped siliconnitride. If the material of the first oxygen-rich dielectric layer 111is silicon oxide, after a deposition process of silicon oxide isperformed, the oxygen source gas may be directly replaced with thenitrogen source gas to form silicon nitride. Before the replacement withthe nitrogen source gas, if the oxygen source gas is retained in thereaction chamber, the oxygen-doped silicon nitride is finally formed. Itshould be noted that the oxygen source gas in the reaction chamber maybe accidentally retained or designedly retained, so as to control theatomic fraction of oxygen in the first silicon-rich dielectric layer112.

In an example in which the first silicon-rich dielectric layer 112 is anoxygen-doped silicon nitride layer, the first silicon-rich dielectriclayer 112 is provided as a silicon-rich oxygen-deficient dielectriclayer, it is necessary to control the atomic fraction of oxygen in thefirst silicon-rich dielectric layer 112 to be greater than 0% and lessthan or equal to 10%, for example, 2%, 4%, 6% or 8%, so that thematerial property of the first oxygen-rich dielectric layer 111 arecloser to that of the first silicon-rich dielectric layer 112, therebyimproving the interface property between them. Specifically, when thematerial of the first oxygen-rich dielectric layer 111 is a material ofnegative electricity, such as aluminum oxide, etc., the doped oxygenatoms make the first oxygen-rich dielectric layer 111 and the firstsilicon-rich dielectric layer 112 have a same element, and the latticeproperty of the first oxygen-rich dielectric layer 111 is close to thatof the first silicon-rich dielectric layer 112, thereby facilitatingreduction of interface defects and stress damage between the firstoxygen-rich dielectric layer 111 and the first silicon-rich dielectriclayer 112.

In some embodiments, when the material of the first oxygen-richdielectric layer 111 is silicon oxide, doped oxygen atoms may not berequired in the first silicon-rich dielectric layer 112 as both thelayers include a same element (i.e., silicon), so that the atomicfraction of oxygen in the first silicon-rich dielectric layer 112 may be0%. In other embodiments, the atomic fraction of oxygen in the firstsilicon-rich dielectric layer 112 is greater than 0% and less than orequal to 7%.

In addition, the doped oxygen atoms may be used for adjusting thepositive electricity and the refractive index of the first silicon-richdielectric layer 112. The more the oxygen atoms, the weaker the positiveelectricity and the lower the refractive index. By doping a certainamount of oxygen atoms, the first silicon-rich dielectric layer 112 hasa relatively strong positive electricity, and meanwhile, the firstsilicon-rich dielectric layer 112 is prevented from being of excessivelystrong positive electricity (which diminishes the field passivationeffect of the first oxygen-rich dielectric layer 111 and the electricalproperty of the emitter 102), and of excessively high refractive index,so as to avoid internal reflection caused by the excessive differencebetween the refractive indexes of the first silicon-rich dielectriclayer 112 and the first oxygen-rich dielectric layer 111.

In some embodiments, the material of the second silicon-rich dielectriclayer 114 includes nitrogen silicide. During determination on atomicfraction of the second silicon-rich dielectric layer 114, it isnecessary to control the second silicon-rich dielectric layer 114 to beof higher refractive index so that the light incident through the secondsilicon-rich dielectric layer 114 vertically falls into the substrate10, and it is necessary to control a smaller difference between therefractive indexes of the second silicon-rich dielectric layer 114 andthe second oxygen-rich dielectric layer 113, thereby suppressinginternal reflection and emission of the light. Based on the aboveconsiderations, the second silicon-rich dielectric layer 114 may includea second silicon nitride material in which a ratio of silicon atoms tonitrogen atoms is in a range of 3.82 to 6.37, for example, 4.35, 4.85,5.35, or 5.85.

Accordingly, in order to make the first silicon-rich dielectric layer112 and the second silicon-rich dielectric layer 114 mainly absorblong-wave light of different wavelengths and as much as possible tosuppress internal reflection and emission of the light passing throughthe different layers, under the condition of the aforementioned ratio ofatoms, the refractive index of the second silicon-rich dielectric layer114 may be in a range of 1.98 to 2.06, for example, 2.00, 2.02, 2.04,and the thickness of the second silicon-rich dielectric layer 114 in thedirection perpendicular to the first surface 10 a may be in a range of20 nm to 50 nm, particularly, 20 nm to 40 nm, for example, 25 nm, 30 nm,or 35 nm. Further, the second silicon-rich dielectric layer 114 shouldbe thick enough to refract the light into the substrate 10, and shouldbe thin enough to prevent applying an excessive stress to the secondoxygen-rich dielectric layer 113 which results in interface defects, andto reduce an overall size of the solar cell.

In some embodiments, the second silicon-rich dielectric layer 114 isdoped with oxygen atoms, but the number of doped oxygen atoms is small,that is, the second silicon-rich dielectric layer 112 is a silicon-richoxygen-deficient dielectric layer (also referred to as a secondsilicon-rich oxygen-deficient dielectric layer), and the doped oxygenatoms are used to alleviate the stress between the second silicon-richdielectric layer 114 and the second oxygen-rich dielectric layer 113.For example, the atomic fraction of oxygen in the second silicon-richdielectric layer 114 is greater than 0% and less than or equal to 10%,particularly, greater than 0% and less than or equal to 7%, for example,2%, 4% or 6%.

In some embodiments, the first silicon-rich dielectric layer 112 and thesecond silicon-rich dielectric layer 114 are silicon-rich layers otherthan the oxygen-doped silicon nitride layers, such as silicon carbidelayers or oxygen-doped silicon carbide layers, or the first silicon-richdielectric layer 112 and the second silicon-rich dielectric layer 114further include other elements besides oxygen, nitrogen, and silicon. Inorder to ensure that the first silicon-rich dielectric layer 112 and thesecond silicon-rich dielectric layer 114 are of higher refractive index,the atomic fraction of silicon in the first silicon-rich dielectriclayer 112 and the second silicon-rich dielectric layer 114 may be in arange of 30% to 70%, for example, 40%, 50% or 60%.

In some embodiments, the atomic fraction of silicon in the firstsilicon-rich dielectric layer 112 is greater than the atomic fraction ofsilicon in the second silicon-rich dielectric layer 114, such that therefractive index of the first silicon-rich dielectric layer 112 ishigher, and thus a gradient of refractive index changes from small tolarge is formed to suppress internal reflection and emission of thelight. For example, in the second silicon-rich dielectric layer 114, theatomic fraction of silicon may be in a range of 30% to 60%, for example,35%, 40%, 45%, 50% or 55%, and a ratio of the atomic fraction of siliconto the atomic fraction of nitrogen may be in a range of 0.46 to 1.87,for example, 0.8, 1.1, 1.4 or 1.7; in the first silicon-rich dielectriclayer 112, the atomic fraction of silicon may be in a range of 40% to70%, for example, 45%, 50%, 55%, 60% or 65%, and a ratio of the atomicfraction of silicon to the atomic fraction of nitrogen may be in a rangeof 0.66 to 2.3, for example, 1, 1.3, 1.6, 1.9 or 2.2.

In some embodiments, the solar cell further includes at least onestacked structure disposed in a direction away from the substrate 10,the stacked structure further includes an oxygen-rich layer and anoxygen-deficient dielectric layer that are sequentially stacked. Thatis, in some embodiments, the solar cell surface may be provided with atleast three stacked structures to enhance the electrical property of theoxygen-rich dielectric layer and the electrical property of theoxygen-deficient dielectric layer.

In some embodiments, the second surface 10 b is further provided with apassivation contact structure including at least a tunneling oxide layer121 and a doped conductive layer 122 that are sequentially disposed in adirection away from the substrate 10. The material of the tunnelingoxide layer 121 is a dielectric material, such as silicon oxide, forachieving interface passivation of the second surface 10 b. A thicknessof the tunneling oxide layer 121 in a direction perpendicular to therear surface 10 b may be in a range of 0.5 nm to 3 nm, for example, 1nm, 1.5 nm, 2 nm, or 2.5 nm. The material of the doped conductive layer122 used to form field passivation may be, for example, doped silicon,which may be one or more of doped polysilicon, doped microcrystallinesilicon or doped amorphous silicon. A type of the doped ions of thedoped conductive layer 122 is the same as a type of the doped ions ofthe base region 101. A thickness of the doped conductive layer 122 inthe direction perpendicular to the rear surface 10 b may be in a range80 nm to 160 nm, for example, 100 nm, 120 nm or 140 nm, and a refractiveindex of the doped conductive layer 122 may be in a range of 3.5 to 4.5,for example, 3.75, 4, or 4.25.

In some embodiments, the doped conductive layer 122 is further providedthereon with a second passivation layer 123 for enhancing reflectioneffect of the incident light on the back of the cell. The secondpassivation layer 123 may be a single-layer structure or a multi-layerstructure in which different sub-layers may be made form a same materialbut different in refractive index, or may be made from differentmaterials. The second passivation layer 123 may include a plurality ofsub-layers, and the plurality of sub-layers gradually decreases inrefractive index in the direction from second surface 10 b to the dopedconductive layer 122, thereby using internal reflection to enhance thereflection effect of the incident light on the back of the cell. Whenthe material of the second passivation layer 123 is silicon nitride, thesilicon nitride sub-layer of higher refractive index has more hydrogenions which may migrate to the second surface 10 b under a diffusionpower due to concentration difference or a thermal power formed by aheat treatment process, so as to passivate interface defects between thesubstrate 10 and the passivation contact structure and thus suppress thecarrier recombination and improve the photoelectric conversionefficiency.

Specifically, the second passivation layer 123 may include a bottompassivation layer, an intermediate passivation layer, and a toppassivation layer that are sequentially disposed, and the bottompassivation layer covers a surface of the doped conductive layer 122.The bottom passivation layer has a refractive index in a range of 2.12to 2.2, for example, 2.14, 2.16, or 2.18, and a thickness in thedirection perpendicular to the second surface 10 b a range of 10 nm to20 nm, for example, 13 nm, 15 nm, or 18 nm. The intermediate passivationlayer has a refractive index in a range of 2.10 to 2.12, for example,2.13, 2.15 or 2.18, and a thickness in a range of 20 nm to 30 nm, forexample, 23 nm, 25 nm or 28 nm. The top passivation layer has arefractive index in a range of 2.09 to 2.10, and a thickness in a rangeof 30 nm to 50 nm, for example, 35 nm, 40 nm or 45 nm. In general, thesecond passivation layer 123 has an average refractive index in a rangeof 2.04 to 2.2, for example, 2.08, 2.12, or 2.16, and a thickness in thedirection perpendicular to the second surface 10 b in a range of 60 nmto 100 nm, for example, 70 nm, 80 nm, or 90 nm.

Further, the solar cell further includes a first electrode 115electrically connected to the emitter 102 and a second electrode 124passing through the passivation layer 123 to electrically connected tothe field passivation layer 122. In some embodiments, the firstelectrode 115 and/or the second electrode 124 may be form by sinteringand printing a conductive paste (silver paste, aluminum paste, orsilver-aluminum paste).

In some embodiments, the oxygen-rich dielectric layer and thesilicon-rich dielectric layer are sequentially disposed. Compared withthe silicon-rich dielectric layer, the oxygen-rich dielectric layer isof higher density, weaker positive electricity and lower hardness, whichcontribute to preventing external ions from diffusing into the substrateand to reducing defect density and stress damage of the emitter, or maybe of stronger negative electricity, which contributes to forming fieldpassivation on the substrate and realizing selective transmission ofcarriers. At least two oxygen-rich dielectric layers are provided, whichmay strengthen any one of the aforementioned effects or make the solarcell have both effects. In addition, compared with the oxygen-richdielectric layer, the silicon-rich dielectric layer generally has ahigher refractive index. The two silicon-rich dielectric layers arespaced from each other, which is advantageous for causing two gradientsof refractive index, so that light of different wavelengths caneffectively enter into the substrate, which improves the absorptionefficiency of the solar cell. Moreover, the atomic fraction of oxygen inthe second oxygen-rich dielectric layer is larger than the atomicfraction of oxygen in the first oxygen-rich dielectric layer, whichcontributes to blocking the external ions or other impurities in theouter layer, avoiding influence on antireflection performance of thefirst silicon-rich dielectric layer, and ensuring a higher efficiencyfor light absorption of the solar cell.

Embodiments of the present disclosure further provide a photovoltaicmodule for converting received light energy into electrical energy.Referring to FIG. 4 , the photovoltaic module includes a cell string(not shown), a package adhesive film 2, and a cover plate 3. The cellstring is formed by connecting a plurality of solar cells 1. The solarcells 1 may be any of the foregoing solar cells (including but notlimited to the solar cells of FIG. 1 ). Adjacent solar cells 1 areelectrically connected by a conductive tape (not shown). The packageadhesive film 2 may be an organic package adhesive film, such as anethylene-vinyl acetate copolymer (EVA) adhesive film, a polyethyleneoctene co-elastomer (POE) adhesive film, or a polyethylene terephthalate(PET) adhesive film. The package adhesive film 2 covers a surface of thecell string for sealing. The cover plate 3 may be transparent orsemi-transparent cover plate, such as a glass cover plate or a plasticcover plate, and the cover plate 3 covers a surface of the packageadhesive film 2 facing away from the cell string. In some embodiments, alight trapping structure is provided on the cover plate 3 to improveutilization of incident light. The light trapping structure may bevaried depend on the cover plate 3. The photovoltaic module is of betterability in current collecting and lower carrier recombination rate,which can achieve higher photoelectric conversion efficiency. Meanwhile,the photovoltaic module has a dark blue or even black appearance in thefront, which is wildly applicable.

Since the package adhesive film 2 and the cover plate 3, when disposedon a rear surface of the solar cell 1, may block or weaken the weakerlight, in some embodiments, the package adhesive film 2 and the coverplate 3 are disposed only on a front surface of the solar cell 1 toavoid such blocking or weakening. Meanwhile, the photovoltaic module canbe fully packaged at its sides, that is, the sides of the photovoltaicmodule is completely covered by the package adhesive film 2, so as toprevent the layers of the photovoltaic module from shifting during thelamination process, and prevent the external environment from affectingthe performance of the solar cell through the side of the photovoltaicmodule, such as water vapor intrusion.

In some embodiments, referring to FIG. 5 , the photovoltaic modulefurther includes an edge sealing member 6 that fixedly packages at leastthe sides of the photovoltaic module. Further, the edge sealing member 6at least fixedly packages to the sides of the photovoltaic module nearthe corners. The edge sealing member 6 may be a high-temperatureresistant adhesive tape. Based on the high-temperature resistance of thehigh-temperature resistant adhesive tape, during the lamination processor during use of the solar cell, the edge sealing member 6 does notdecompose or fall off, which ensures reliable package of thephotovoltaic module. In some embodiments, the high-temperature resistantadhesive tape is affixed not only to the sides of the photovoltaicmodule, but also to the front and rear surfaces of the photovoltaicmodule, which prevents the layers of the photovoltaic module fromshifting during the lamination process and avoids deformation of thephotovoltaic module under stress. Embodiments of the present disclosurefurther provide a method for manufacturing a solar cell. Referring toFIG. 6 to FIG. 10 and FIG. 1 , FIG. 4 to FIG. 10 and FIG. 1 areschematic structural diagrams corresponding to various steps of themethod for manufacturing a solar cell according to the embodiment of thepresent disclosure.

Referring to FIG. 6 , a base region 101 is provided and textured at bothsides.

Specifically, a N-type substrate is cleaned, and a pyramid-texturedsurface is formed thereon by wet chemical etching. The pyramid-texturedsurface can reduce light reflection on the surface of the base region101, thereby improving absorption and utilization of the light on thebase region 101 and improving conversion efficiency of the solar cell.In some embodiments, the base region 101 is made from monocrystallinesilicon, and has a thickness in a range of 60 μm to 240 μm, inparticular, 60 μm, 80 μm, 90 μm, 100 μm, 120 μm, 150 μm, 200 μm, or 240μm, and a resistivity in a range of 0.3 ohm·cm to 2 ohm·cm.

It should be noted the specific operation of the texturing process isnot limited herein. For example, the texturing process is not limited tothe wet chemical etching. When the base region 101 is made from N-typemonocrystalline silicon, an alkaline solution, such as potassiumhydroxide solution, may be used for the texturing process. Theanisotropic corrosion of NaOH solution contributes to preparation of apyramidal microstructure. The pyramidal microstructure may betetrahedral, approximately tetrahedral, pentahedral, approximatelypentahedral, or the like. In addition, the texturing process may bechemical etching, laser etching, mechanical process, plasma etching,etc. The pyramidal microstructure enables the screen-printed metal pasteto be better filled in the microstructure when forming the electrode,thereby obtaining better contact of the electrodes, effectively reducingresistance of the cells connected in series and improving the fillingfactor. An overall reflectivity of the solar cell may be less than 10%by controlling the morphology of the pyramidal microstructure.

Referring to FIG. 7 , a P-type emitter 102 is formed.

After texturing of both sides of the base region 101, a first surface 10a of the base region 101 is subjected to a boron diffusion treatment toform a P-type emitter 102 which occupies a part of a surface layer ofthe base region 101 for receiving the light. The P-type emitter 102 andthe N-type base region 101 constitute a substrate 10. The P-type emitter102 has a diffusion square resistance in a range of 130Ω to 150Ω and asurface diffusion concentration in a range of E18 to E19.

It should be noted that in the boron diffusion treatment, borosilicateglass is additionally generated on a front surface (i.e., the firstsurface 10 a), a rear surface and a side surface of the base region 101,and thus prevents the surfaces of the base region 101 from being damagedin some subsequent processes. That is, the additional borosilicate glassmay serve as a mask layer for the base region 101. A boron source forthe boron diffusion treatment includes liquid boron tribromide, andduring the boron diffusion treatment, a phrase change occurs from amicrocrystalline silicon phase to a polycrystalline silicon phase.

Referring to FIG. 8 , a planarization process (e.g., polishing) isperformed on the rear surface of the base region 101.

The rear surface is at a side of the solar cell facing away from thelight. Due to the planarization process, the rear surface is planarizedto form a flat surface for depositing layers thereon, i.e., the secondsurface 10 b. During the planarization process, the borosilicate glasson the rear surface is removed.

In some embodiments, before a polishing process, the method furtherincludes the following steps: the borosilicate glass on the surface ofthe base region 101 is removed with a prepared mixed acid which includesa hydrofluoric acid solution having a mass fraction in a range of 0.1%to 10%, a sulfuric acid solution having a mass fraction in a range of10% to 20% and a nitric acid solution having a mass fraction of 25% to50%, with a pickling time in a range 10 s to 180 s and a picklingtemperature in a range of 7° C. to 20° C.; and then the pickled rearsurface 10 b is washed with water and dried. It should be noted that aporous structure may be formed on the rear surface 10 b of the substrate10 after pickling.

In some embodiments, the rear surface 10 b may be polished with analkali solution. Specifically, the surface 10 b is cleaned with thealkali solution having a mass fraction in a range of 5% to 15% to removeporous silicon. The rear surface 10 b is roughened by sprayingmicrodroplets of the alkali solution on the rear surface 10 b, and thenpre-cleaned with hydrofluoric acid having a mass fraction in a range of5% to 10%. The rear surface 10 b is polished with a polishing solution,with a polishing temperature in a range of 70° C. to 80° C. and apolishing time of less than 260 s, and the polishing solution includesNaOH having a mass fraction in a range of 1% to 15%, KOH having a massfraction in a range of 1% to 15% and additive having a mass fraction ina range of 0.5% to 2.5%. Organic components are removed from the etchingsolution with a mixed solution which includes potassium hydroxide havinga mass fraction in a range of 5% to 15% and hydrogen peroxide having amass fraction in a range of 15% to 40%. Then the polished substrate 10is washed with water and dried.

In some embodiments, since the rear surface 10 b is of low concentrationin boron, etching with the alkali solution can effectively improveetching efficiency. The alkali solution includes an organic base and/oran inorganic base. The inorganic base may be NaOH, KOH, Ga(OH)2, orNH3.H2O. The organic base may be triethylamine, nitrophenol, pyridine,quinine, colchicine, or the like. The additive in the polishing solutionmay be a buffer solution including sodium sulfonate, maleic anhydride,alkyl glycoside, and the like. In some embodiments, a weight loss of thesubstrate 10 is less than 0.3 g after being polished, and the rearsurface 10 b may have a preset structure by controlling the polishingtime and the polishing temperature.

Referring to FIG. 9 a , a tunneling oxide layer 121 and a dopedconductive layer 122 are formed.

In some embodiments, the tunneling oxide layer 121 is formed by means ofa deposition process. Specifically, the material of the tunneling oxidelayer 121 includes silicon oxide, the deposition process includes achemical vapor deposition process, and the thickness of the tunnelingoxide layer 121 in a direction perpendicular to the second surface 10 bis in a range of 1 nm to 2 nm, for example, 1.2 nm, 1.4 nm, 1.6 nm, or1.8 nm. In other embodiments, the tunneling oxide layer may be formed bymeans of an in-situ generation process. Specifically, the tunnelingoxide layer may be formed in-situ by a thermal oxidation process and anitric acid passivation process based on a silicon substrate.

In some embodiments, the tunneling oxide layer 121 is formed bydeposition on the rear surface 10 b by means of a variable temperatureprocess and a chemical vapor deposition method. During deposition, aheating rate is in a range of 0.5° C./min to 3° C./min, for example,1.0° C./min, 1.5° C./min, 2.0° C./min, or 2.5° C./min, etc., adeposition temperature is in a range of 560° C. to 620° C., for example,570° C., 590° C., or 610° C., etc., and a deposition time is in a rangeof 3 min to 10 min, for example, 4 min, 6 min, or 8 min, etc.

In some embodiments, after the tunneling oxide layer 121 is formed,intrinsic polysilicon is deposited to form a polysilicon layer, andphosphorus ions are doped by ion implantation and source diffusion toform an N-type doped polysilicon layer as a doped conductive layer 122.The thickness of the doped conductive layer 122 in a directionperpendicular to the second surface 10 b may be in a range of 80 nm to160 nm, for example, 100 nm, 120 nm, or 140 nm.

When the tunneling oxide layer 121 and the doped conductive layer 122are formed by means of the deposition process, since the first surface10 a of the base region 101 is protected by the borosilicate glass as amask layer on the front surface, limitation to the deposition region onthe rear surface through the mask is not required during the depositionprocess, and the borosilicate glass on the front surface and the siliconoxide and polysilicon deposited on the front surface can be removedsimultaneously in a subsequent process. In this way, no additional maskis required, which is advantageous for reducing process steps,shortening process period, and lowering process cost. In otherembodiments, when the interface passivation layer is formed by mean ofthe in-situ generation process, only polysilicon is deposited on theborosilicate glass on the front surface of the substrate.

In some embodiments, deposition of the tunneling oxide layer 121 and thepolysilicon layer and doping of the polysilicon layer are performed in alow-pressure chemical vapor deposition apparatus. The specific steps areas follows: firstly, the alkali-polished substrate 10 is placed in thedeposition apparatus; an oxygen source (which may be oxygen, nitrousoxide, ozone, for example) in a range of 20 L to 60 L is introduced; thechamber within the deposition apparatus is heated to a temperature in arange of 560° C. to 620° C. at a heating rate in a range of 0.5° C./minto 3° C./min for a deposition time in a range of 3 min to 10 min, so asto form the tunneling oxide layer 121; after the introduction of oxygenis completed, the temperature is controlled to be constant, and thensilane gas of an appropriate amount is introduced to form thepolysilicon layer; finally, the polysilicon layer is doped in situ toform the doped conductive layer 122.

Referring to FIG. 10 , a first passivation stack is formed on the firstsurface of the substrate 10, and includes a first oxygen-rich dielectriclayer 111, a first silicon-rich dielectric layer 112, a secondoxygen-rich dielectric layer 113, and a second silicon-rich dielectriclayer 114 that are sequentially disposed. The first oxygen-richdielectric layer 111 covers the first surface 10 a.

In some embodiments, the redundant borosilicate glass, silicon oxide,and polysilicon coated on the first surface 10 a of the substrate 10need to be removed prior to forming the first passivation stack. Inother embodiments, the redundant borosilicate glass and polysiliconcoated on the first surface of the substrate need to be removed prior toforming the first passivation stack.

Further, in other embodiments, after the redundant material is removed,a thin silicon oxide layer is then generated on the first surface of thesubstrate. The thin silicon oxide layer is formed by natural oxidation,thermal oxidation, wet oxidation, atomic layer deposition,plasma-enhanced chemical vapor deposition, and the like. A thickness ofthe thin silicon oxide layer in the direction perpendicular to thesubstrate surface is in a range of 0 to 3 nm, for example, 1 nm, 1.5 nm,or 2 nm.

In some embodiments, the first oxygen-rich dielectric layer 111, thefirst silicon-rich dielectric layer 112, the second oxygen-richdielectric layer 113, and the second silicon-rich dielectric layer 114may be formed by processes, such as chemical vapor deposition,low-pressure chemical vapor deposition, plasma-enhanced chemical vapordeposition (including direct plasma deposition and indirect plasmadeposition), magnetron sputtering, and the like. An atomic fraction ofoxygen in the second oxygen-rich dielectric layer 113 is greater thanthat in the first oxygen-rich dielectric layer 111.

In some embodiments, the atomic fraction of oxygen in the firstoxygen-rich dielectric layer is in a range of 40% to 70%, particularly40% to 60%. The atomic fraction of oxygen in the first silicon-richdielectric layer is greater than 0% and less than or equal to 10%,particularly greater than 0% and less than or equal to 7%. The atomicfraction of oxygen in the second oxygen-rich dielectric layer is in arange of 30% to 80%, particularly 50% to 80%. The atomic fraction ofoxygen in the second silicon-rich dielectric layer is greater than 0%and less than or equal to 10%, particularly greater than 0% and lessthan or equal to 7%.

The first oxygen-rich dielectric layer 111 may include at least twooxygen-rich sub-layers. The material of the first oxygen-rich dielectriclayer 111 includes at least one of aluminum oxide, silicon oxide,gallium oxide, hafnium oxide, titanium oxide, silicon oxynitride, andthe like. If the material of the first oxygen-rich dielectric layer 111is silicon oxynitride, the reactant therefor may be silane, nitrousoxide, and ammonia, and the first oxygen-rich dielectric layer 111 mayhave a refractive index in a range of 1.61 to 1.71 and a thickness inrange of 8 nm to 20 nm. If the material of the first oxygen-richdielectric layer 111 is silicon oxide, the reactant therefor may be atleast one of silane, nitrous oxide, and oxygen, and the firstoxygen-rich dielectric layer 111 may have a refractive index in a rangeof 1.58 to 1.61 and a thickness in a range of 2 nm to 15 nm. If thematerial of the first oxygen-rich dielectric layer 111 is aluminumoxide, the reactant therefor may be trimethylaluminum and water, and thefirst oxygen-rich dielectric layer 111 may have a refractive index in arange of 1.71 to 1.78, and a thickness in a range of 1 nm to 20 nm.

The material of the first silicon-rich dielectric layer 112 may be atleast one of silicon nitride and silicon carbide. When the material ofthe first silicon-rich dielectric layer 112 is silicon nitride, thefirst silicon-rich dielectric layer 112 may be designed to include twoor three sub-layers gradually changed in refractive index according toactual requirements. That is, the silicon nitride sub-layers graduallydecrease in refractive index in a direction away from the substrate 10.Further, the reactant therefor may be silane and ammonia. A ratio of thenumber of silicon atoms to the number of nitrogen atoms in the firstsilicon-rich dielectric layer 112 may be in a range of 0.66 to 2.3. Thefirst silicon-rich dielectric layer 112 may have a refractive index inthe range of 2.02 to 2.2, and a thickness in a range of 20 nm to 50 nm.

The material of the second oxygen-rich dielectric layer 113 may be oneof silicon oxide and silicon oxynitride, the reactant therefor includessilane, nitrous oxide and ammonia. A ratio of the number of oxygen atomsto the number of nitrogen atoms in the second oxygen-rich dielectriclayer 113 may be in a range of 2.58 to 7.58. The second oxygen-richdielectric layer 113 may have a refractive index in the range of 1.56 to1.62, and a thickness in a range of 5 nm to 20 nm.

The material of the second silicon-rich dielectric layer 114 may be oneof silicon nitride and silicon carbide. When the material of the secondsilicon-rich dielectric layer 114 is silicon nitride, the secondsilicon-rich dielectric layer 114 may be designed to include two orthree sub-layers gradually changed in refractive index according toactual requirements. That is, the silicon nitride sub-layers graduallydecrease in refractive index in a direction away from the substrate 10.Further, the reactant therefor may be silane and ammonia. A ratio of thenumber of silicon atoms to the number of nitrogen atoms in the secondsilicon-rich dielectric layer 114 may be in a range of 0.46 to 1.78. Thesecond silicon-rich dielectric layer 114 may have a refractive index inthe range of 1.98 to 2.06, and a thickness in a range of 20 nm to 50 nm.

Referring to FIG. 1 , a second passivation layer 123 is formed on thedoped conductive layer 122, and a first electrode 115 and a secondelectrode 124 are formed.

When the material of the second passivation layer 123 is siliconnitride, the second passivation layer 123 may be designed to includetwo, three or four sub-layers gradually changed in refractive indexaccording to actual requirements. That is, the silicon nitridesub-layers gradually decrease in refractive index in a direction awayfrom the substrate 10. Further, the reactant therefor may be silane andammonia. A ratio of the number of silicon atoms to the number ofnitrogen atoms in the second passivation layer 123 may be in a range of3.82 to 6.37. The second passivation layer 123 may have a refractiveindex in the range of 2.04 to 2.2, and a thickness in a range of 60 nmto 100 nm.

After the second passivation layer 123 is formed, the first electrode115 and the second electrode 124 may be formed by a process, such asmetallization, screen printing, and high-temperature sintering. Further,after the electrodes are formed, a light annealing treatment is alsorequired, that is, the solar cell sheet is heated at a temperature in arange of 400° C. to 700° C. (for example, 500° C., or 600° C.) for atime in a range of 1 min to 6 min (for example, 2 min, 3 min, 4 min, or5 min), and then treated simultaneously at a temperature in a range of150° C. to 400° C. (for example, 200° C., 250° C., 300° C., or 350° C.)and under a light intensity in a range of 1 to 6 solar light intensities(for example, 2, 3, 4, or 5 solar light intensities) for a time in arange of 1 min to 6 min.

Those skilled in the art should appreciate that the aforementionedembodiments are specific embodiments for implementing the presentdisclosure. In practice, however, various changes may be made in theforms and details of the specific embodiments without departing from thespirit and scope of the present disclosure. Any person skilled in theart may make their own changes and modifications without departing fromthe spirit and scope of the present disclosure, so the protection scopeof the present disclosure shall be subject to the scope defined by theclaims.

What is claimed is:
 1. A solar cell, comprising: a substrate, whereinthe substrate is made from silicon-based material and has a firstsurface and a second surface opposite to each other; a first passivationstack disposed on the first surface and including a first oxygen-richdielectric layer, a first silicon-rich dielectric layer, a secondoxygen-rich dielectric layer, and a second silicon-rich dielectric layerthat are sequentially disposed in a direction away from the firstsurface, wherein an atomic fraction of oxygen in the first oxygen-richdielectric layer is in a range of 40% to 70%, the first silicon-richdielectric layer includes oxygen atoms and an atomic fraction of oxygenin the first silicon-rich dielectric layer is greater than 0% and lessthan or equal to 10%, an atomic fraction of oxygen in the secondoxygen-rich dielectric layer is in a range of 50% to 80%, and the secondsilicon-rich dielectric layer includes oxygen atoms and an atomicfraction of oxygen in the second silicon-rich dielectric layer isgreater than 0% and less than or equal to 10%, wherein the atomicfraction of oxygen in the first oxygen-rich dielectric layer is lessthan the atomic fraction of oxygen in the second oxygen-rich dielectriclayer, wherein the first oxygen-rich dielectric layer includes analuminum oxide material, wherein the atomic fraction of oxygen in thesecond oxygen-rich dielectric layer is greater than an atomic fractionof silicon in the first silicon-rich dielectric layer and greater thanan atomic fraction of silicon in the second silicon-rich dielectriclayer, the atomic fraction of silicon in the second silicon-richdielectric layer is in a range of 30% to 60%, and the atomic fraction ofsilicon in the first silicon-rich dielectric layer is in a range of 40%to 70%; a tunneling oxide layer disposed on the second surface; a dopedconductive layer disposed on a surface of the tunneling oxide layer; anda second passivation layer disposed on a surface of the doped conductivelayer.
 2. The solar cell according to claim 1, wherein the atomicfraction of oxygen in the first oxygen-rich dielectric layer is in arange of 40% to 60%, the atomic fraction of oxygen in the firstsilicon-rich dielectric layer is greater than 0% and less than or equalto 7%, and the atomic fraction of oxygen in the second silicon-richdielectric layer is greater than 0% and less than or equal to 7%.
 3. Thesolar cell according to claim 1, wherein the first oxygen-richdielectric layer includes an aluminum oxide layer and a siliconoxynitride layer, and the aluminum oxide layer is positioned between thesilicon oxynitride layer and the substrate.
 4. The solar cell accordingto claim 1, wherein a ratio of the number of oxygen atoms to the numberof aluminum atoms in the aluminum oxide is in a range of 0.6 to 2.4. 5.The solar cell according to claim 1, wherein a refractive index of thefirst oxygen-rich dielectric layer is higher than a refractive index ofthe second oxygen-rich dielectric layer.
 6. The solar cell according toclaim 1, wherein the first oxygen-rich dielectric layer further includesa silicon oxide material, a refractive index of the first oxygen-richdielectric layer is in a range of 1.58 to 1.61, and a thickness of thefirst oxygen-rich dielectric layer in a direction perpendicular to thefirst surface is in a range of 2 nm to 15 nm.
 7. The solar cellaccording to claim 1, wherein the first oxygen-rich dielectric layerfurther includes a silicon oxynitride material, a refractive index ofthe first oxygen-rich dielectric layer is in a range of 1.61 to 1.71,and a thickness of the first oxygen-rich dielectric layer in a directionperpendicular to the first surface is in a range of 8 nm to 20 nm. 8.The solar cell according to claim 1, wherein a refractive index of thefirst oxygen-rich dielectric layer is in a range of 1.71 to 1.81, and athickness of the first oxygen-rich dielectric layer in a directionperpendicular to the first surface is in a range of 1 nm to 20 nm. 9.The solar cell according to claim 1, wherein the second oxygen-richdielectric layer includes a silicon oxynitride material, a refractiveindex of the second oxygen-rich dielectric layer is in a range of 1.56to 1.62, and a thickness of the second oxygen-rich dielectric layer in adirection perpendicular to the first surface is in a range of 5 nm to 20nm.
 10. The solar cell according to claim 1, wherein a refractive indexof the first silicon-rich dielectric layer is higher than a refractiveindex of the second silicon-rich dielectric layer.
 11. The solar cellaccording to claim 10, wherein the refractive index of the firstsilicon-rich dielectric layer is in a range of 2.02 to 2.2, and therefractive index of the second silicon-rich dielectric layer is in arange of 1.98 to 2.06.
 12. The solar cell according to claim 1, whereina material of the first silicon-rich dielectric layer includes a firstsilicon nitride material, and a ratio of the number of silicon atoms tothe number of nitrogen atoms in the first silicon nitride material is ina range of 0.66 to 2.3.
 13. The solar cell according to claim 12,wherein a refractive index of the first silicon-rich dielectric layer isin a range of 2.02 to 2.2, and a thickness of the first silicon-richdielectric layer in a direction perpendicular to the first surface is ina range of 20 nm to 50 nm.
 14. The solar cell according to claim 1,wherein a material of the second silicon-rich dielectric layer includesa second silicon nitride material, and a ratio of the number of siliconatoms to the number of nitrogen atoms in the second silicon nitridematerial is in a range of 0.46 to 1.87.
 15. The solar cell according toclaim 14, wherein a refractive index of the second silicon-richdielectric layer is in a range of 1.98 to 2.06, and a thickness of thesecond silicon-rich dielectric layer in a direction perpendicular to thefirst surface is in a range of 20 nm to 50 nm.
 16. The solar cellaccording to claim 1, wherein a refractive index of the secondpassivation layer is in a range of 2.04 to 2.2, and a thickness of thesecond passivation layer in a direction perpendicular to the secondsurface is in a range of 60 nm to 100 nm.
 17. A photovoltaic modulecomprising: a cell string including a plurality of solar cells connectedwith each other; a package adhesive film configured to cover a surfaceof the cell string; a cover plate configured to cover a surface of thepackage adhesive film facing away from the cell string; wherein each ofthe plurality of solar cells includes: a substrate, wherein thesubstrate is made from silicon-based material and has a first surfaceand a second surface opposite to each other; a first passivation stackdisposed on the first surface and including a first oxygen-richdielectric layer, a first silicon-rich dielectric layer, a secondoxygen-rich dielectric layer, and a second silicon-rich dielectric layerthat are sequentially disposed in a direction away from the firstsurface, wherein an atomic fraction of oxygen in the first oxygen-richdielectric layer is in a range of 40% to 70%, the first silicon-richdielectric layer includes oxygen atoms and an atomic fraction of oxygenin the first silicon-rich dielectric layer is greater than 0% and lessthan or equal to 10%, an atomic fraction of oxygen in the secondoxygen-rich dielectric layer is in a range of 50% to 80%, and the secondsilicon-rich dielectric layer includes oxygen atoms and an atomicfraction of oxygen in the second silicon-rich dielectric layer isgreater than 0% and less than or equal to 10%, wherein the atomicfraction of oxygen in the first oxygen-rich dielectric layer is lessthan the atomic fraction of oxygen in the second oxygen-rich dielectriclayer, wherein the first oxygen-rich dielectric layer includes analuminum oxide material, wherein the atomic fraction of oxygen in thesecond oxygen-rich dielectric layer is greater than an atomic fractionof silicon in the first silicon-rich dielectric layer and greater thanan atomic fraction of silicon in the second silicon-rich dielectriclayer, the atomic fraction of silicon in the second silicon-richdielectric layer is in a range of 30% to 60%, and the atomic fraction ofsilicon in the first silicon-rich dielectric layer is in a range of 40%to 70%; a tunneling oxide layer disposed on the second surface; a dopedconductive layer disposed on a surface of the tunneling oxide layer; anda second passivation layer disposed on a surface of the doped conductivelayer.
 18. The photovoltaic module according to claim 17, furthercomprising: an edge sealing member fixedly packaging at least the sidesof the photovoltaic module.
 19. The photovoltaic module according toclaim 17, wherein the atomic fraction of oxygen in the first oxygen-richdielectric layer is in a range of 40% to 60%, the atomic fraction ofoxygen in the first silicon-rich dielectric layer is greater than 0% andless than or equal to 7%, and the atomic fraction of oxygen in thesecond silicon-rich dielectric layer is greater than 0% and less than orequal to 7%.